The development of root surface caries has been repeatedly demonstrated to be a significant dental health problem of our adult population. The disease afflicts about 50% of adults by age 45 and its prevalence and severity increase markedly with increasing age. The significance of the problem is exacerbated by the increased retention of the natural dentition as a result of declining coronal caries and the well-known difficulty in effectively restoring root surface lesions. Previous studies in our laboratories in the past 2 years, plus a variety of reports from other investigators during the past few years, have clearly demonstrated the effectiveness of fluoride in the prevention of root surface caries. These studies have demonstrated that the ingestion of fluoridated water as well as the daily application of extremely concentrated fluoride gels decrease the formation of root surface caries by at least 50%. In vitro studies have also suggested that fluoride can remineralize early root caries. However, the identification of the most effective and efficient use of fluoride to both prevent root caries formation and remineralize existing lesions must await a greater understanding of the mechanism of this cariostatic activity. This proposed continuation project will utilize an experimental animal root caries model developed by the investigators for studying root caries prevention, in combination with a state-of-the-art microradiographic, computer-enhanced image analysis procedure for quantifying remineralization of root surface lesions. These procedures will be used primarily to investigate the mechanism of action of luoridated water and other commonly-used fluroide measures (rinses, dentifrices, professional applications) with regard to both the prevention of root caries and the remineralization of such lesions. Information generated will be particularly useful in understanding the mechanism of action of these measures, identifying the cariostatic potential of combinations of fluoride measures for root caries prevention and arrestment (remineralization), and the designing of future clinical trials to assess the benefits of these measures to our adult citizens.